I say BS for Co2, page-82

You have to look a few days before the eruption, because that's when most of the gas comes out. Popocatapetl (Mexico) and Santiaguito (Guatemala) both erupted in the last day or so. Looking back through the past two weeks...



Right on cue - and if you watch the animated version you can see that these aren't just noise flukes - there are clear sources at these sites. Of course, every volcano is different - the amount of gas that comes out will vary according to all manner of parameters - local geochemistry, porosity of the cap, how long since the last eruption, etc. - but the idea that volcanoes in general emit carbon monoxide is entirely uncontroversial.